1. Field of the Invention
The present invention relates to a subminiature chip fuse capable of being directly soldered to a printed circuit board for use.
2. Description of the Prior Art
In conventional chip fuses, a fusible element is stretched between metal terminal plates placed apart at a certain distance on a plane in such a manner that the end surfaces of the metal terminal plates oppose each other (for instance, refer to the official gazette of Japanese Utility Model Laid-Open No. 119546/1984) or wherein a pair of main electrodes are provided at ends of a flat chip board with a pair of auxiliary electrodes being provided at an intermediate portion between the main electrodes, and wires are connected between these main and auxiliary electrodes so as to be bonded thereto (for instance, refer to the official gazette of Japanese Patent Laid-Open No. 172626/1987).
In the former type of conventional chip fuse described above, only a narrow gap is feasible between the terminals in which a fusible element is extended due to the small size of a fuse body which is required in a chip fuse. As a result, in relation to the time-current characteristics thereof, an excessively fast fuse response tends to be exhibited, thereby causing a risk of the fusible element being fused by a rush current generated by switching during a normal operation.
In addition, the narrow gap necessitates the use of a short fusible element, which results in a fusible element having a low resistance. This requires a fusible element having a smaller diameter to be employed when attempting to produce a fuse with a lower current value. However, the extremely small diameter which is required for such a fusible element is impossible to manufacture. Even though a fusible element with such an extremely small diameter thereof may be manufactured, it would be extremely difficult for it to be assembled into a fuse.
In the latter type of conventional chip fuse, the surface of the wires is covered with a transparent resin that is curved in a lens fashion, and this transparent resin deprives the wires of Joule's heat. This makes the fusing performance thereof unstable. In addition, since there are provided only a pair of auxiliary electrodes, as in the case of the former chip fuse, an excessively fast fuse response is exhibited, and it is not possible to modify an such response time.